FAGL15QA408YPThin Section Angular Contact Ball Bearing, 4.500 x 5.000 x 1/4 in, Square 1/4 x 1/4 in Section, Type A Single Row, Open, Brass Separator

Product Description

What this part is

A thin section angular contact ball bearing, 4.500 in bore x 5.000 in outside diameter x 0.250 in wide. It is the direct equivalent of Kaydon KA045AR0 and Silverthin SA045AR0 — open, single row, Type A angular contact, with 1/8 in balls in a one-piece machined brass pocket separator, ABEC Class 1.

Correcting the source data

The previous title gave the width as 1/2 in while the description said 0.25 in. The description was right and the title was wrong: the width is 1/4 in.

The proof is geometric and needs no datasheet. Thin section bearings are built on a square cross section, so (outside diameter − bore) ÷ 2 must equal the width. Here (5.000 − 4.500) ÷ 2 = 0.250 in of wall each side, which matches a 1/4 in width exactly. A 1/2 in width would require a 1/2 in wall per side and therefore a 5.500 in outside diameter — not a thin section geometry at all. Silverthin’s own datasheet for the equivalent SA045AR0 independently confirms 4.500 x 5.000 x 1/4 in. The title has been corrected.

This matters practically: a buyer ordering to the old 1/2 in figure would have designed a housing 0.25 in too deep and specified the wrong axial clamp stack.

Decoding the designation

L15 — FAG thin section series prefixQ — the cross-section code. Q, R, S and T are ascending sections mapping to Kaydon’s letters: Q = 1/4 x 1/4, R = 5/16 x 5/16, S = 3/8 x 3/8, T = 1/2 x 1/2. The Q is what makes this the 1/4 in sectionA — Type A, single row angular contact, thrust in one direction408 — bore in whole inches plus sixteenths, not hundredths: 4 and 08/16 = 4.500 in. Corroborated by SKF, which uses the identical digits in its FPAA408 equivalentYP — one-piece machined brass circular-pocket separator

On provenance: no published Schaeffler or FAG document giving the Q/R/S/T section table could be located, so this decode is derived from independently verified dimensional data points plus the Silverthin interchange rather than from a FAG datasheet. The dimensions are firmly published; the letter mapping is a well-supported deduction.

Published ratings and mounting data

Static radial load capacity: 1,660 lbfDynamic radial load capacity: 637 lbf (Kaydon method); 1,410 lbf on the ISO 281:1990 basis, shown for comparison only — the two methods are not interchangeableStatic thrust load capacity: 4,810 lbfDynamic thrust load capacity: 1,580 lbfLand diameters: L1 4.686 in, L2 4.814 in, L3 (counterbore) 4.865 inBall diameter: 1/8 inMaximum fillet radius cleared: 0.025 inRace width tolerance: +0.000 / −0.005 inPrecision: ABEC Class 1Weight: 0.210 lbCorners: normally chamfered

Radial and thrust ratings are not additive — a combined load must be checked against a combined-load calculation rather than against either column alone.

Ball count and contact angle are not published and are deliberately omitted. On contact angle that is a property of the product rather than a research gap: Kaydon states a Type A bearing “requires the application of thrust to establish contact angle,” so the angle is preload-dependent and has no fixed catalogue value. Any source quoting a degree figure for a Type A thin section is quoting something the manufacturer does not publish.

What these specs mean in practice

Note how small the numbers are relative to the bearing’s size — 637 lbf dynamic radial from a five-inch bearing. That is the thin section trade in plain view: you give up load capacity to get a very thin radial wall and a very large open bore. The design driver is almost always something passing through the middle, such as a hollow shaft, cable bundle, slip ring, laser path or coolant line. Hence their use in robotics joints, gimbals, rotary and index tables, medical imaging gantries, semiconductor wafer handlers and optical positioners. At 1/8 in ball diameter this is one of the finer sections in the range, so it is a light-duty precision positioning bearing, not a load-carrying one.

Fitting notes

Thin rings are flexible and will faithfully adopt the out-of-roundness of whatever you clamp them into — by far the most common cause of premature failure in this class, and more acute at this 1/4 in section than at heavier ones. Housing bores and shaft seats must be round and flat to a tighter standard than a conventional bearing would tolerate, the structure must be rigid, and clamping load must be applied uniformly around the circumference rather than through a few bolts. Respect the 0.025 in maximum fillet radius — it is small.

Type A carries thrust in one direction only; on a reversing application a single Type A unloads on the reverse stroke, so you need a duplex pair (BR0 or FR0) or a four-point contact bearing (XP0). Being open, it has no lubricant retention at all.

Interchange guidance

Direct equivalents: Kaydon KA045AR0, Silverthin SA045AR0, SKF FPAA408, NSK NBA11406, NTN KYA045, RBC KA045AR0, SSB RA045AR0, INA CSEA045 — the INA reference being a Schaeffler in-house sibling rather than a third-party substitute.

Related but not substitutes: SA045CP0 / KA045CP0 (radial contact), SA045XP0 / KA045XP0 (four-point contact), SA045BR0 (duplex back-to-back), SA045FR0 (duplex face-to-face), JSA045CP0 (sealed radial contact), JSA045XP0 (sealed four-point). Unlike the larger sections, sealed variants are catalogued at this bore.

Central Surplus also stocks FAG L15TA708YP, L15RA700YP and L15RA400YP from this same family. Note that these are different sections, not just different bores — do not cross-quote specifications between them.